Conventional stamping machines and processes are carried out on a moving web including a preprinted substrate material. To add design, security, or informational elements that are part of a completed web, a decal or section of foil constituting such an element is stamped out of the foil onto the web at defined locations. The stamping operation is typically accomplished by means of a rotary stamper that is provided with a die mounted onto its outer surface. The die comes into contact with a separate foil tape bearing the decals or design elements that are to be transferred, and transfers one such element to the substrate web by pressing down on it against the web. In some operations, heat may be applied to achieve the desired effect.
A disadvantage of such a process lies with the expense of the foil tape. The tape is often very expensive in relation to the underlying substrate, and therefore adds disproportionately to the overall cost of the competed web. Costs become accentuated as end-users process expensive tapes such as holograms and other metallic decals onto the material with which their product is packaged. Typically, the decal stamped from the tape onto the substrate web occupies only a very small fraction of the length of each individually completed design on the substrate. In the area at which the foil is stamped, the foil preferably has a velocity that matches the velocity of the facing web so as to properly register with the web. A conventional method of assuring such a match in velocities includes the step of feeding the foil through the apparatus and to the stamping area at a uniform velocity equal to the velocity of the web. However, the so-called continuous feed approach inevitably wastes most of the foil, for only that portion of the foil that registers with the die when the die cycles over the desired section of the web is ever used. The remainder of the foil is discarded as waste.
Various schemes have been proposed to make more efficient use of the foil. Generally speaking, they all present some structural arrangement by which the speed of the foil at the die is altered between the web velocity, at which the foil can most easily be stamped and registered onto the web substrate, and a lesser velocity. In other words, such arrangements aim to make better use of the foil by feeding it in an intermittent manner to the die area, as opposed to the continuous feed arrangement described above. Conventional means for accomplishing intermittent feed employ a rotary stepper motor to pivot a rocker arrangement about which the tape is wound. The rotary movement of the rocker arms imparts a component of velocity to the foil wound about the rocker arms. Unfortunately, the use of rotary motion to control the linear position of a moving foil presents errors and uncertainties in the position of the foil that exacerbates the problem of registration between the foil and the substrate web, which is of utmost importance in many applications. Also, the use of such structure adds to the maintenance costs of the apparatus.
There remains a need for a foil stamping apparatus that makes efficient use of the foil and that provides enhanced registration capabilities.